Photodecomposition of Liquid Water with TiO₂‐Supported Noble Metal Clusters

Abstract

SummaryRh-and Ru-loaded Ti02-particles were produced from cluster precursors (Rh6 (CO)16, Ru3 (CO),,) and their activity in mediating H20-decomposition through band-gap excitation was investigated. Activity increases in the order Ru < RuO2 < Rh * Rh203. Bifunctional Rh/Ru02-loaded Ti02 exhibits optimal performance with overall light-to-chemical-energy conversion efficiency of 0.13%. Lack of Orappearance in the gas phase during photolysis observed with closed systems is due to photo-uptake of O2 by the Ti02-particles. In alkaline solution the capacity for 02-uptake is surprisingly high and the nature of the stored O2 is tentatively identified as a p-peroxo-bridged Ti-species.Introduction. -Supported metal catalysts have previously been shown to be active in microheterogeneous systems that achieve H20-cleavage by visible and UV light [l-lo]. Noble metals deposited onto semiconductors such as Ti02 [l-31171, SrTi03 [4-61 and CdS [8] [9] appear to be particularly promising. To achieve optimum activity in H20-decomposition, high dispersion of the noble metal onto the support is generally required. This increases the H20-reduction and -oxidation rates per unit mass of catalyst employed. Moreover, there is recent evidence [ 111 that the recombination of H2 with O2 might be affected by the size of the noblemetal particle. Thus, it has been shown that the reduction of O2 on Pt-cathodes tested for fuel cell application is almost totally inhibited once the Pt-crystallite size decreases below 30 A. Reduction of O2 to H 2 0 is an undesirable back reaction in devices that afford simultaneous generation of H2 and O2 by light. In close relation to this effect stands the observation of Turkevich et al. [I21 that the activity of Pt-colloids in the catalytic decomposition of H202 drops from an extremely high value (close to that of catalase) to practically zero when the particle size was decreased below 30 A.A particularly favorable situation for H20-decomposition would arise if these ultrafine Pt-particles, though inactive in 02-reduction, would still remain powerful catalysts for the generation of H2 from H20. That this concept is viable was shown by us in a recent investigation [13] where a systematic test of the effect of Pt-particle size on the rate of photochemical H2-generation in Pt/Ti02-dispersions was carried

Facile synthesis of monodisperse polymer/SiO2/polymer/TiO2 tetra-layer microspheres and the corresponding double-walled hollow SiO2/TiO2 microspheres

“…This phenomenon was opposite to the observation from Brown and Darwent when they studied the photooxidation reactions of colloidal TiO 2 with MO as a probe, in which the photooxidation of MO obeyed an initial burst followed by a slower steady decay [24]. They attributed this inhibition to the surface absorbed peroxide formed by reduction of O 2 and oxidation of surface hydroxyl groups [25]. It has been shown by Boonstra and Mutsaers that H 2 O 2 is chemisorbed onto TiO 2 at low pH to give a surface peroxo complex [26].…”

The Work Function of TiO2

“…Figure 3). This shoulder is likely attributed to peroxo (O 2− 2 ) surface species, like for example in bridging oxygen dimers [62]. The stoichiometric anatase (001) and (101) surfaces show no shoulder in the O 1s emission after annealing in vacuum at 473 K. The surface peroxo species observed after oxygen plasma treatment at ox-a(001) and ox-a(101) is therefore effectively removed by annealing.…”

Fermi Level Positions and Induced Band Bending at Single Crystalline Anatase (101) and (001) Surfaces: Origin of the Enhanced Photocatalytic Activity of Facet Engineered Crystals

“…[13] In our work, the an-(001) does not form this reconstruction, since the lattice O was incorporated again by the O plasma treatment. [16] Furthermore, peroxo species on the surface were found to transform to a so-called bridging dimer at the lattice site via interaction with surface or subsurface O vacancies. The emission of Ti2p spectra for sp-(101) shows a strong low binding energy emission of Ti 3+ and Ti 2+ shifted to the main emission line of Ti 4+ by around 1.7 and 3.5 eV, respectively, while sp-(001) exhibits sharp symmetric main lines consisting of a Ti 4+ oxidation state.…”